The purpose of the map is to show how the city's water consumption has grown in conjunction with the city's expanding footprint. If you use the timeline beneath the map you can animate through the satellite images and see how the city has spread further and further out into the surrounding desert. Check-out how Lake Mead in particular seems to have visibly shrunk in size in just the last decade.

The map was created as part of ProPublica's superb Killing the Colorado interactive, which explores how man is engineering the death of this great American river.

You can also explore the rapid growth of Las Vegas over time on Time's Timelapse map. Timelapse allows you to create a timelapse sequence from satellite images (from
1984 to 2012) for anywhere on Earth.The application comes with a number
of default views that allow you to view timelapse animations of
satellite images showing the sprawling growth of Las Vegas, the building
of Dubai, the shrinking of the Mendenhall Glacier and the drying-up of
Lake Urmia.

Timelapse can be a little hard to navigate. You need to scroll down the page a little until the 'Explore the World' link appears in the header element at the top of the page. Click on the 'Explore the World' link and you can then choose from any of the default satellite animations or search for any location in the world.